Ge, a promising n-type thermoelectric oxide composite

We have studied the chemical, structural and transport properties of a series of In2O3 based samples with germanium doping (from 0 to 15 atom%). X-ray diffraction and scanning electron microscopy studies show that the solubility limit of Ge in In2O3 is very small and that additions of more than about 0.5 atom% Ge lead to the presence of In2Ge2O7 inclusions. The electrical conductivity is strongly enhanced by Ge doping with best values exceeding 1200 S cm−1 at room temperature. On the other hand, the thermopower decreases with Ge addition, but the thermoelectric power factor remains higher than that of undoped In2O3 and is close to 1 mW m−1 K−2 at 1100 K in In1.985Ge0.015O3. The thermal conductivity is strongly reduced by Ge additions. The dimensionless figure of merit ZT reaches 0.1 at 1273 K in In2O3 and exceeds 0.45 at 1273 K in composite compounds with nominal composition In1.8Ge0.2O3.